Travelling Wave Kicker Magnets with Sharp Rise and Less Overshoot

As an alternative to the classical design of travelling wave kicker magnets, a structure with a fairly simple additional feature was developed and investigated. This modification was based on the following considerations. The shape of the rise of the magnetic field in a travelling wave kicker is determined by two main factors: i) the shape of the applied current pulse, and ii) the propagation characteristics of the magnet structure. In the PSB kicker system1), kiloampere pulses with a rise-time of ~ 10 ns are obtained by means of ferriteloaded pulse steepening lines2). Measurements show, however, that pulses with this rise-time are severely distorted as they travel along the various kicker magnets. It was therefore thought worth while to examine whether any improvements might be possible, other than the classical remedies of increasing the number of cells or raising the characteristic impedance. To this end a typical magnet module (Fig. 1) was measured using RF techniques and its dispersion curve compared to calculations for various possible equivalent circuits. After concluding that the mutual inductance between cells was a dominant factor, the kicker was modified by adding inductive coupling of opposite sign. This considerably improved the dispersion curve, with a corresponding increase in the phase and group velocities for high frequencies. Although attenuation still produces some distortion, pulse measurements confirmed that the pulse transmission was substantially improved.